1. Field of the Invention
The invention relates to electrical stimulation of the body, and in particular a system, device and method for controlled and monitored electrical stimulation of the brain, through the afferent cranial nerves linked to the oral cavity.
2. Description of the Prior Art
Brain plasticity or neuroplasticity is the brain's capability of restructuring itself, leading to functional recovery after brain damage. Neuroplasticity can be induced through neurostimulation, also called neuromodulation. Various methods are used to provide neurostimulation, like Cognitive-Behavior Therapy (CBT), Transcranial Magnetic Stimulation (TMS), as well as various types of electrical stimulation, like Transcranial Direct Current Stimulation (tDCS), Transcranial Alternating Current Stimulation (tACS), Transcranial Random Noise Stimulation (tRNS), and Cranial Nerve Non-Invasive Neuromodulation (CN-NINM).
Electrical stimulation has been increasingly used in the last decades, in the rehabilitation of patients suffering from neurological conditions, the most widely used method being tDCS. Electrical stimulation is also used for sensory augmentation and substitution, more specifically for visual or balance impaired individuals. tDCS is anon-invasive method of neuromodulation, known to induce lasting changes in the brain, These neuroplastic changes are achieved by increasing or decreasing the firing rates of the neurons, through the hyperpolarization or depolarization of the resting membrane's potential.
Various devices have been developed recently for the purpose of inducing neuroplasticity non-invasively, through electrical stimulation. Companies like Soterix™, Magstim™, Nexalin™, NeuroConn™, and Mind Alive™ have developed transcranial electrical stimulation devices, while Wicab™ has developed an intraoral stimulation device, the Tongue Display Unit (TDU), for sensory substitution and augmentation, as well as CN-NINM. The TDU delivers an alternative current signal to selected regions of the tongue through an array of intraoral electrodes. This stimulation is used to provide exogenous information cues, and has been shown to induce neuromodulation via the cranial nerves. Cognitive-Behavior Therapy has been found to benefit from the addition of learning-induced neuroplasticity via computerized cognitive training.
A major challenge related to tDCS is the relatively high impedance of the skull and the skin, that limits the current delivered through trans-cutaneous electrodes placed on or near the scalp; only about 50% of the stimulation current is routed through the brain tissue. The higher the impedance, the more difficult is to ensure a focused targeted delivery of current. The TDU, on the other hand, has a different type of problem: it was designed to use saliva to facilitate the delivery of the AC stimulus, thus it is missing the capability to deliver DC stimulus, which requires a physical barrier in order to avoid the deposition of material from the electrode(s) to the human tissue, through electrolysis. The TDU is only delivering stimuli to the surface of the tongue, in particular the tip of the tongue, stimulating only to the cranial nerves connected to these regions. None of these devices are providing feedback regarding the position of the electrode(s) as well as the quality of the contact between electrodes and the tissue.